DE19506980C2 - Control method for the fuel injection of an internal combustion engine, which is provided with a catalyst for reducing NO¶x¶, and a device for carrying out this control method - Google Patents

Description

The present invention relates to a method for controlling the fuel injection of an internal combustion engine and to a control device for fuel injection for performing the method, and in particular to a method for controlling the fuel injection of an internal combustion engine or a combustion engine, which or which with a catalyst for reducing NO _x , which reduces the NO _x concentration of the exhaust gas to the lowest possible level without using a plurality of catalysts, and is provided with a control device for fuel injection for carrying out the method.

The status of Technology is based on this referred to DE 38 27 780 A1.

Although the exhaust gas cleaning ability of an exhaust gas purification technique according to an invention, which e.g. B. disclosed in Japanese Patent Laid-Open No. 63-100919 (Kokai), which uses a NO _x -reducing catalyst, is effective when a lean air / fuel mixture is applied, the exhaust gas purifying ability of the same technique is not reliable, when a stoichiometric air / fuel mixture with a relatively low oxygen concentration is used. A similar technique is described in Japanese Patent Laid-Open No. 5-133260 (Kokai).

These known techniques require at least two types of catalysts, namely a NO _x -reducing catalyst and an oxidation catalyst or a three-way catalyst. Although three-way catalysts have been used and effective three-way catalysts are available, there has been a desire to develop effective NO _x reducing catalysts.

The present invention has been made based on the fact that a three-way catalyst made by applying Rh, Pt and / or Pd and La to a porous support has NO _x reducing ability when lean air / Fuel mixture is used for combustion, and that the NO _x reducing ability of the three-way catalyst deteriorates with the operating time of the internal combustion engine in a lean air / fuel mixture.

It is an object of the present invention to provide a control method for the fuel injection, which is capable of the three-way catalyst sator in terms of its ability to take full advantage, as well as a Fuel injection control device for executing the fuel injection control method create.

This object is achieved according to the invention through a regulatory procedure in accordance with Claim 1 and according to a device Claim 5 reached.

The present invention measures the operating time of an internal combustion engine in a lean air / fuel mixture and supplies the lean air / fuel mixture and measures a stoichiometric air / fuel mixture or a fuel-rich air / fuel mixture alternately in one Time ratio to keep the NO _x reduction ratio at a high level while supplying the lean air / fuel mixture. For example, in an LA4 mode, the NO _x reduction ratio is the ratio of the operating time of the internal combustion engine in a lean air / fuel mixture to that in a stoichiometric air / fuel mixture (hereinafter referred to as the "LS ratio" is called) dependent. It is therefore important to regulate the LS ratio.

The NO _x reducing ability of the three-way catalyst made by applying Rh, Pt and / or Pd and La to a porous support is effective when a lean air / fuel mixture is supplied to an internal combustion engine NO _x -reducing ability of the three-way catalyst deteriorates with the operating period of the engine at the lean air / fuel mixture, and the original NO _x -reducing ability of the three-way catalyst can be restored when the three-way -Catalyst is exposed to an exhaust gas that is emitted by the internal combustion engine operating in a stoichiometric air / fuel mixture. Therefore, the LS ratio must be properly controlled so that the three-way catalyst can function effectively when the internal combustion engine is operating on a lean air / fuel mixture.

The above and other objectives, features and advantages of the present Invention will become more apparent from the following description in Connection with the accompanying drawings, in which:

Fig. 1 is a schematic view of an air / fuel supply system by a control apparatus for fuel injection in a preferred embodiment according to the present invention, there is regulated;

Fig. 2 is a block diagram of the fuel injection control device for controlling the air / fuel supply system of Fig. 1;

Fig. 3 is a graph showing the variation in NO _x reducing behavior of a three-way catalyst with time when the air / fuel ratio is controlled by the fuel injection control device shown in Fig. 2;

Fig. 4 is a graph showing the dependence of the NO _x reduction ratio in which the three-way catalyst used in the present invention reduces NO _x on the air / fuel ratio;

Fig. 5 is a graph showing the variation of the NO _x reduction ratio in which the three-way catalyst; used in the present invention shows NO _x reduced with time;

Fig. 6 is a diagram showing the relationship between the NO _x -Redu zierungsverhältnis, wherein the three-way catalyst which is employed in the present invention, NO _x is reduced, and the LS-ratio shows;

Fig. 7 is a diagram for assistance in explaining the desired NO _x reduction ratio of the catalyst used in the present invention;

Fig. 8 is a diagram showing an appropriate air / fuel ratio as a function of parameters indicating the operating condition of the internal combustion engine;

. 9 is a flowchart of Regelungsver be executed with the control device of Figure 2 for the fuel injection is Fig driving of the fuel injection. and

Fig. 10 is a diagram to support the explanation of the control method for the fuel injection of the present inven tion in connection with parameters that indicate the operating state of the internal combustion engine.

Referring to FIG. 1, an internal combustion engine 7 (hereinafter simply referred to as an "engine") is provided with an air / fuel supply system that is controlled by a fuel injection control device in a preferred embodiment according to the present invention. The air / fuel supply system has an air intake system and a fuel injection system. The air inlet system comprises: an air filter 1 with an air inlet opening 2 through which air is sucked in by the suction effect of the engine 7 , an air flow meter 3 , an air inlet line 4 , a throttle valve 5 with a throttle valve element for regulating the inlet air flow rate, a collector 6 and an intake manifold 8 for sharing the intake air to the cylinders (only one of which is shown) of the engine 7 . The fuel injection system has: a fuel tank 9 , which the fuel such. B. contains gasoline, a fuel pump 10 for pumping up the fuel from the fuel tank 10 and dispensing the fuel by pressure, a fuel damper 11 , a fuel filter 12 , fuel injectors 13 (only one of which is shown) and a fuel pressure regulator 14 for maintaining the fuel pressure within a specified range. The fuel is injected into the branch pipes of the intake manifold 8 through the fuel injection valves 13 , which are respectively provided on the branch pipes of the intake manifold 8 . The fuel injection system is regulated or controlled by the control device 15 for the fuel injection.

The air flow meter 3 outputs a signal representing an intake air flow rate to the control device 15 for the fuel injection. A throttle sensor 18 detects the opening of the throttle valve 5 and outputs a signal, which represents the opening of the throttle valve 5 , to the control device 15 for the fuel injection. A distributor 16 is provided with a crank angle sensor, which contains a reference angle signal REF, which characterizes the crank angle of the crankshaft of the engine 7 , and an angle signal POS for detecting the engine speed to the control device 15 for the fuel injection. An oxygen sensor 21 , which is provided in the exhaust manifold of the engine 7 , detects the oxygen concentration of the exhaust gas for estimating the actual air / fuel ratio and outputs a detection signal to the control device 15 for fuel injection. The oxygen sensor 21 is unable to determine the actual air / fuel ratio. The oxygen sensor 21 provides an output of approximately 1 V when an air / fuel mixture rich in fuel, ie an air / fuel mixture with an air / fuel ratio which is less than a stoichiometric air / fuel ratio , and provides an output of the order of 0.2 V when a lean air / fuel mixture, ie an air / fuel mixture with an air / fuel ratio greater than a stoichiometric air / fuel Ratio is fed. It is most desirable to use an air / fuel ratio sensor that is capable of actually determining the air / fuel ratio of the air / fuel mixture, if any, in place of the oxygen sensor 21 . The exhaust pipe is provided with a three-way catalytic converter 20 , which can convert the toxic components including CO, hydrocarbons and NO _{x of} the exhaust gas into non-toxic substances. The three-way catalyst is able to reduce NO _x , which is explained below.

As shown in FIG. 2, the control device 15 for the fuel injection has as basic components an MPU (micro-processor unit = microprocessor unit), an EPROM (erasable programmable ROM = erasable programmable ROM), a RAM and an I / O interface on. The MPU processes and inputs signals provided by sensors for detecting the values of parameters that characterize the operating state of the engine 7 , including an engine speed sensor and an engine load sensor, which are supplied to the engine via the I / O interface Pulse signal to the fuel injection valves 13 . The pulse width of the pulse signal is determined based on the values of the parameters so that an air / fuel mixture of a desired air / fuel ratio is supplied to the engine 7 . The MPU also provides an ignition coil control signal to an ignition coil 17 to control the injection times. Thus, the control device 15 for the fuel injection controls both the air / fuel ratio and the injection times.

By way of example, FIG. 3 shows the variation of the NO _x reducing ability of the three-way catalytic converter 20 with the operating time of the engine 7 , in which the measured NO _x reduction ratio is measured upwards on the vertical axis and the time to the right is measured on the horizontal axis. In Fig. 3, the time intervals indicated at "L" are those in which a lean air / fuel mixture is supplied, and at "S" are those in which a stoichiometric air / fuel mixture is supplied . As can be clearly seen from Fig. 3, the NO _x reduction ratio is almost equal to 100% while the stoichiometric air / fuel mixture is supplied. If a lean air / fuel mixture is supplied, the NO _x reduction ratio gradually decreases over time and in the worst case decreases to a value on the order of 50% or less. The three-way catalyst 20 is made by bringing Rh, Pt and / or Pd and La onto a porous support. The NO _x reducing ability of the three-way catalyst depends on the respective amounts of these catalytic metals, and the NO _x reducing ability can be increased by applying additional catalytic metals to the porous support. In general, the NO _x reducing ability of the three-way catalyst decreases with engine operating time with a lean air / fuel mixture, and it is theoretically impossible to change any of these tendencies, which will be discussed in more detail below with reference to is Fig. 4 and 5.

Fig. 4 shows the dependence of the NO _x reduction ratio on the air / fuel ratio when the engine 7 is operating in a stationary state. When an air / fuel mixture rich in fuel is supplied, that is, when the air / fuel ratio is in a range of an air / fuel ratio in which the air / fuel ratio is smaller than a stoichiometric air / fuel - Ratio of 14.7, the NO _x reduction ratio is essentially 100%. As the air / fuel ratio rises above the stoichiometric air / fuel ratio, the NO _x reduction ratio gradually decreases and actually decreases to zero when the air / fuel ratio is about 22. As shown in FIG. 5, the NO _x reduction ratio at initial operation is very high after the air / fuel ratio goes from a high air / fuel ratio that is higher than the stoichiometric air / fuel ratio to a low one Air / fuel ratio has been changed, which is lower than the stoichiometric air / fuel ratio, because the three-way catalyst 20 is able to absorb NO _x . In this state, the NO _x reduction ratio decreases with time and actually decreases to zero in about two minutes. The high initial NO _x reduction ratio can be restored by changing the air / fuel ratio from the high air / fuel ratio, which is higher than the stoichiometric air / fuel ratio, to the low air / fuel ratio. which is lower than the stoichiometric air / fuel ratio. Thus, the NO _x -reducing ability of the three-way catalyst 20 can be cyclically changed by changing the air-fuel ratio between a low air-fuel ratio and a high air-fuel ratio.

The NO _x reduction ratio will now be further examined with reference to FIG. 6. In view of the NO _x reducing ability of the three-way catalyst 20 , assume that the duration of supply of a lean air / fuel mixture is two minutes, for example, and the LS ratio is varied; ie the duration of the supply of a lean air / fuel mixture is fixed, while the duration of the supply of a stoichiometric air / fuel mixture is varied. As is clear from Fig. 6, the NO _x reduction ratio varies with the LS ratio. If e.g. For example, the NO _x concentration of the exhaust gas of the engine 7 with a NO _x concentration is limited, which is specified in the standard emission while the engine 7 is operating in the LA4 mode, a desired NO _x -Reduzierungsverhältnis on the basis of Known NO _x concentration of the exhaust gas of the engine 7 can be calculated. In the case illustrated in FIG. 7, the desired NO _x reduction ratio is about 80%. Referring again to FIG. 6, the NO _x reduction ratio is 80% when the LS ratio is 50%; that is, when the LS ratio is set to 50%, the NO _x concentration of the exhaust gas conforms to the value specified in the emission standard.

Fig. 8 shows the required from the motor 7 for different operating states of the air / fuel ratios. An area A is an area in which a lean air / fuel mixture is supplied in which λ << 1 and the air / fuel ratio is 22 or above; an area B is an area in which an air / fuel mixture is supplied in which λ = 1; and an area C is an area of supply of an air-fuel mixture rich in fuel, in which λ <1, in order to secure the necessary power output and to protect the engine 7 . The areas A, B and C can be specified in a single map or in different maps. Generally, air / fuel mixtures are supplied in areas A and B for exhaust gas tests when operating in the LA4 mode. The extent or size of the area A depends on the excess power output of the engine 7 .

An air-fuel ratio control method according to the present invention will now be described hereinafter with reference to FIG. 9, in which only steps shown in connection with the present invention including that of an engine control system are shown.

In step 101, parameters which characterize the operating state of the engine 7 , such as, for. B. Engine speed Ne and engine load L are measured, and one of the ranges A, B and C shown in Fig. 8 is selected. In step 102, a desired air / fuel ratio is determined. In step 103, a query is made to see whether an inequality λ << 1 is satisfied or not. If the answer in step 103 is negative, the air / fuel ratio control process is ended. If the answer is affirmative in step 103, a timer begins to measure the time T (λ <1) of the duration of a condition in area A in step 104. A request is then made in step 105 as to whether a defined period of time {X}, e.g. B. two minutes during which a lean air / fuel mixture is supplied, as described in connection with FIG. 5, has passed. If the set period of time {X} has not yet passed, the control operation is continued to maintain the air-fuel ratio for the area A. When the specified time period {X} has passed, the air / fuel ratio is set to a stoichiometric air / fuel ratio (λ 1) in step 106. Even if the air / fuel ratio is changed, the engine 7 must be controlled by the engine control device so that the operating state of the engine 7 does not change at all. In step 107, a timer measures the time T (λ <1) of the duration of supply of a stoichiometric air / fuel mixture. In step 108, the time period T (λ <1) measured by the timer is compared with a reference time period K _* T (λ <1). If the period T (λ <1) is shorter than the reference period K _* T (λ <1), the procedure returns to step 106 to continue the control operation. If the time period T (λ <1) measured by the timer is longer than the reference time period K _* T (λ <1), the timers are reset. In the reference period K _* T (λ <1), K is the LS ratio, which is optionally determined in accordance with the NO _x concentration specified in the emission standard and the desired NO _x reduction ratio. Fig. 10 is a characteristic diagram of a K = LS ratio for engine load and engine speed.

Although the embodiment has been described on the assumption that the air / fuel ratio of the lean air / fuel mixture is 22 , the air / fuel ratio of the lean air / fuel mixture may optionally be used in conjunction with the LS ratio be determined.

Although the invention in its preferred example with a certain Clearly, there have been many degrees of specificity described Changes and variations possible. It should therefore be understood that the present invention otherwise than specifically here described can be carried out without their scope and Deviate mind.

Claims (4)

1. Control method for fuel injection, which regulates the air / fuel ratio of an air / fuel mixture to be supplied to an internal combustion engine, which is provided in its exhaust system with a catalyst for reducing NO _x , characterized in that a first air / Fuel mixture of a stoichiometric or a fuel-rich air / fuel ratio and a second air / fuel mixture of a fuel-lean air / fuel ratio are supplied alternately during respective predetermined time intervals. 2. The fuel injection control method according to claim 1, wherein the ratio K of the time interval in which the first air / fuel mixture is supplied to the time interval in which the second air / fuel mixture is supplied, optionally based the NO _x concentration of the exhaust gas of the internal combustion engine, the NO _x concentration specified in an emission standard, and the NO _x reduction ratio of the catalyst for reducing NO _{x is} determined. 3. Control method for fuel injection according to claim 1, at which the ratio K of the time interval in which the first air / fuel mixture is supplied at the time interval in to which the second air / fuel mixture is supplied, accordingly  Parameters are determined which determine the operating state of the ver label internal combustion engine. 4. Apparatus for performing the method according to claim 1, 2 or 3, characterized by an oxygen sensor ( 21 ) for estimating the actual air / fuel mixture, which is provided in an exhaust manifold of the internal combustion engine ( 7 ) and which has a corresponding signal Control device ( 15 ) for determining the air / fuel mixture and the injection time interval of the fuel supplies.